The home secretary has said politicians cannot be cowed following Friday’s fatal attack on MP Sir David Amess.
Priti Patel’s comments came after she laid flowers, alongside Prime Minister Boris Johnson and Labour leader Sir Keir Starmer, at the scene of the stabbing in Leigh-on-Sea, Essex.
Police are treating the attack as a terrorist incident, which may be linked to Islamist extremism.
A 25-year-old British man is being held on suspicion of murder.
Sir David, a Conservative MP since 1983, was holding one of his regular Friday meetings with his constituents at Belfairs Methodist Church when he was stabbed multiple times.
The 69-year-old was married with four daughters and a son. He is the second MP to be killed in recent years, following the murder of Labour MP Jo Cox in July 2016.
Speaking at Southend police station, Ms Patel paid tribute to Sir David as a “man of the people” who was killed doing “a job he loved”.
She said security measures were being put in place to protect MPs – but insisted they would carry on serving the country unimpeded.
“We will carry on, we live in an open society, a democracy,” she said.
“We cannot be cowed by any individual or any motivation… to stop us from functioning, to serve our elected democracy.”
Ms Patel maintained a balance could be found to allow face-to-face meetings with constituents to continue.
Some MPs held their regular constituency surgeries on Saturday as normal. However, others have raised concern for their safety at sessions where anyone can attend.
Conservative MP Tobias Elwood – who came to the aid of a stabbed police officer during the 2017 terror attack in Westminster – suggested MPs speak to constituents on the phone or over Zoom for the time being, rather than meeting face-to-face.
And Kim Leadbeater, the sister of Mrs Cox, said her partner had asked her to stand down as MP for Batley and Spen after Sir David’s death.
Veteran Labour MP Harriet Harman said she would write to the prime minister to ask him to back a Speaker’s Conference – a type of cross-party inquiry – to review parliamentarians’ safety.
Local police forces are contacting every MP to discuss their personal safety and the security at events they plan to attend.
The police investigation is being led by the Metropolitan Police’s counter terrorism team.
Officers have been searching two addresses in the London area and police said they were not seeking anyone else over the death.
The force believes the man, who is in custody in Essex, acted alone but inquiries are continuing.
Government sources told the BBC he was a British national who, from initial inquiries, appeared to be of Somali heritage.
BBC security correspondent Frank Gardner says Whitehall officials are saying the arrested man was not on a database of terror suspects.
The UK’s threat level remains at “substantial”, meaning a terror attack is likely.
Scotland Yard’s decision that the killing of Sir David Amess was an act of terrorism confirms that, on the basis of what they know so far, the killer was motivated to use violence to further their cause.
There’s no public suggestion from investigations at the moment that there is a specific additional threat to MPs. But detectives and colleagues in MI5 will be delving deeply into the life of the suspect to understand how he reached this mindset – and whether this was an attack by a “lone actor” or someone who is part of a network.
Secondly, it confirms the initial conclusion that there would need to be more resources thrown at the investigation.
Behind the scenes, a wider range of detectives and support staff will now have been brought into action. If officers have recovered the suspect’s mobile phone, they will now be forensically examining its contents to uncover potential evidence of mindset and planning.
A phone – and any bank cards – will also help detectives track the suspect’s movements in the days and weeks before the incident.
That in turn leads them to CCTV, so they can build a three-dimensional view of his life.
Tributes to Sir David have been pouring in from politicians as well as his local constituents.
The prime minister described him as “one of the kindest, nicest, most gentle people in politics”, with an “outstanding record of passing laws to help the most vulnerable”.
Labour’s Sir Keir said it was a “dark and shocking day”, adding that the country had “been here before” with the death of Jo Cox.
Father Jeff Woolnough, a parish priest who led a mass on Friday evening in Sir David’s memory, described him as a “great, great guy” and said faith communities had “lost their greatest supporter”.
Members of Southend-On-Sea’s Muslim community said, in a joint statement, his death was an “indefensible atrocity” and that Sir David would be remembered for his warmth, selflessness and kindness.
Attack casts shadow over Leigh-on-Sea
By Orla Moore & Richard Smith
The mood in Leigh-on-Sea, which Sir David represented for decades, is one of bewilderment.
As police and global media descend upon the usually quiet Essex town, people have gathered to pay tributes outside the Belfairs Methodist Church where the long-standing MP was attacked.
Resident Audrey Martin remembers him as “an absolute gentleman” who took time out to speak to her when she first moved to the area from Scotland.
“He just had this aura about him,” she says.
And constituent Lorraine Migliorini highlights Sir David’s work for children and young people with special educational needs.
“He was genuinely interested and listened to them which was fantastic,” she says. “He got things done.”
Julie Everitt, who has co-ordinated a vigil for him, says she would “always remember him for his genuine smile” and his passion for animal rights.
“He would go on campaigns, he was against the badger cull, he was against trophy hunting and fox hunting,” she says.
“He was a good gentleman, he had a good heart.”
Read more from Orla and Richard at the scene here.
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